FIG. 1 is a partially cross-sectional side view illustrating an example of a miniature motor to which this invention is applied. In FIG. 1, reference numeral 31 refers to a case made of a metallic material, such as mild steel, formed into a bottomed hollow tubular shape, and having a permanent magnet 32 of an arc-segment shape, for example, fixedly fitted to the inner circumferential surface thereof. Numeral 33 refers to a case cover made of a thermoplastic resin material and formed into such a shape that the case cover 33 can be fitted to an open end of the case 31. Numeral 34 refers to a rotor consisting of an armature 35 facing the permanent magnet 32, and a commutator 36 rotatably supported by bearings 37 and 38 each provided on the case 31 and the case cover 33.
Numeral 39 refers to brush arms of an electrically conductive material formed into a plate shape, having at the free ends thereof brushes 40 making sliding contact with the commutator 36, and provided inside the case cover 33. Inside the case cover 33 also provided are input terminals 41 electrically connected to the brush arms 39, through which power is fed from an external d-c power source to the armature 35 via the brush arms 39, the brushes 40 and the commutator 36.
In a miniature motor having the aforementioned construction, when current is fed to the armature 35, rotating force is imparted to the armature 35 disposed in a magnetic field generated by the permanent magnet 32 fixedly fitted to the inner circumferential surface of the case 31. Thus, the rotor 34 is caused to rotate, driving various pieces of equipment connected to the rotor 34.
Such a miniature motor often employs a means for reducing electrical noise in which one of the input terminals 41 is connected to the case 31 via a ground terminal 42 made of an electrically conductive material and formed into a flat plate shape, as shown in FIG. 2. There also is another type of electrical-noise reducing means in which a capacitor 44 is connected across a pair of the input terminals 41 via lead wires 43, as shown in FIG. 3.
In the constructions shown in FIGS. 2 and 3 above, an additional space must be provided inside the equipment or apparatus powered by the miniature motor since the component members of the aforementioned means for reducing electrical noise, such as the ground terminal 42 or the capacitor 44, is installed outside the miniature motor. Furthermore, a mounting space more than necessary has to be provided in the equipment or apparatus because the shape, dimensions and mounting position of the component members of the aforementioned means for reducing electrical noise are not known beforehand by the manufacturer of the equipment or apparatus.
In addition, since the aforementioned means for reducing electrical noise has no common component members, if different types of components are required, separate jigs, tools and operators have to be used. This leads to lowered production efficiency.
The construction shown in FIG. 3 requires the troublesome work of connecting the lead wires 43 of the capacitor 44 to the input terminals 41. That is, soldering work necessary for connecting these components, wiring and cutting operations of the lead wires 43 require a certain degree of skills because the capacitor 44 has to be mounted in an extremely limited space. This results in increased time and manhours, leading to high manufacturing cost. Moreover, soldering in a confined space tends to make the state of soldered connection unstable, resulting in soldered joints lacking in resistance to vibration or impact during service and lowered reliability in electrical connection.
To overcome these problems, the Applicant already proposed a miniature motor having such a construction that electronic components are interposed in series across a pair of input terminals via a spring member made of an electrically conductive material (Japanese Utility Model Application No. Hei-3 (1991)-25151). This improvement invention has made it possible to easily and positively assemble capacitors and other electronic components into a case cover, and realized reduced cost due to easy assembly operation.
Even this improvement invention, however, has certain problems. That is, because of its construction that two capacitors are simultaneously held by a spring member, the improvement invention has a problem that when only one capacitor is needed, the balance of the spring member is deteriorated, leading to failure of stable electrical contact. In the construction where a means of grounding one of the input terminals to the case 31 is used in conjunction with the capacitors, the ground terminal 42 has to be mounted outside the miniature motor, as shown in FIG. 2, thus posing the aforementioned space problem.